Wireless receiving system



May 17, 1938T J. ROBINSON 2,117,680 y `WIRELESS RECEIVING SYSTEM Filed Nov. 2, 1934 2 Sheets-Sheet l IN1/5N 'TOR May 17, 1938. J, R0B|N5QN`1 2,117,680 WIRELESS RECEIVING SYSTEM Filed NOV. 2, 1954l 2 ShQts-Sheet 2 FILTER PHASE ADJUSTER 'FILTER MA n nece VER 4Z M EZ,

f I AERIAL cowrnm.. l 'PHASE DJUSTER l E6 l 1 V+- I @E y 'l 410 Y M l Y FILTER .i0 I l slsNAL. AcceP-ro FnLrER 411 sewn. AccEPToR i@ l f/e//ar 9 ffy# Patented May 17, 1938 d NiTED STATES PATENT OFFICE 2,117,680 WIRELESS RECEIVING SYSTEM James Robinson, London, England Application November 2, 1934, Serial No. 751,205 In Great Britain November 7, 1933 9 Claims. (Cl. IZ50-20) This invention is for improvements in or relatinterference signals obtained from the aerials in ing to wireless receiving systems and the primary approximately the same phase for the wanted object of the invention is to provide a high degree signals whereby the heterodyne beat interference of selectivity in reception more especially for signals are combined in out-of phase relationship the reduction of heterodyne interference produced and with diminished resultant effect. In one 5 by the interaction between the carrier wave of the form there iS prOVided means (i. e. Comprising wanted signals and the carrier waves of the other a rectier) at each aerial for detecting the signals. By this invention use is made of the modulation signals and means for transferring conditions of normal modulated carrier wave the received signals to a receiver common to all 1c transmission wherein the transmission frequenthe aerials fOr COmbining the received signals l0 cies arrive at a receiving system in their normal Wanted and unwanted signals arriving from phase relationship. By the expression mdudilerent directions at one of the aerials aforelated carrier wave transmission I mean a carsaid and closely adjacent as regards their carrier rier wave which is interrupted or altered in any frequencies produce an undesired heterodyne beat l5 manner according to the intelligence to be transeffect- The same signals arriving at another Of l5 mitted and l: include transmissions in which the the aerials also produce the same heterodyne beat carrier component' is partially or completely supnote, but there will be a phase difference between pressed at the transmitter such as single side the heterodyne notes produced in the two aerials band systems and is reinstated at the receiver due t0 the difference in path distance between by a local oscillator or is built up by means 0f the aerials for the wanted and the unwanted sig- 20 a receiver of low damping, nals. Thus by combining the signals collected at According to the invention the method of rethe several aerials the wanted signals may be ceiving modulated carrier wave transmissions ccmbined sensibly arithmetically, Whereas the incomprises producing a plurality of wave path terfering or heterodyne beat eiects are combined dillerences as between the wanted transmission Vectclially With the result that the latter intcrand an interfering transmission of such relative ference is minimized and may fOr all practical frequency as to cause a heterodyne beat interpurposes be eliminated- The aerials 0f Which ference, receiving a plurality of portions of the there may be two or preferably more than tWO wanted and interfering signals in different phase may be spaced in any desired manner and for example may be arranged in a straight line with 3o ferences of the transmissions and combining these unifcrm spacing 0r in a circle. portions of the signals in the accumulative sense Accciding t0 a feature 0f the inVentiOn the for the wanted signals whereby the heterodyne signal-accepting means at each 0f the aerials beat elfect is diminished due to the different phase comprises a frequency ccnverting device for relationships which consequently occur between changing the frequency 0f the carrier-Waye t0 35 the received portions of the interfering signals. ancthcr frequency fOr the transfer 0f the signals The invention also comprises the method of t0 the majcr receiving means ccmmOn t0 all the receiving modulated carrier wave transmissions aerials- The transfer Of the signals frcm the which comprises receiving on a plurality of spaced signal-accepting means at each aerial t0 the o aerials both a wanted signal and an interfering maier receiving means may be eiected by means 40 signal arriving from a differ-ent direction and ci lines 0r by means 0f Wireless links using, fOr

producing a heterodyne interference, and comcXample, a supcrscnic carrier-frequency fOr this bining all the received signals at a single receiver purposewhereby the wanted signals are cumulated but Preferably and mcre especially Where the the phase-differences of the various heterodyne aerials are spaced ccnsidcrablc distances apart beats at the different aerials causes their total means is prcVided, fOr eXample in each 0f the effect to be diminished. connections between the aerials and the major The invention further comprises a receiving receiving apparatus, fOr the relative adjustment system for modulated carrier wave transmissions 0f the phase Of the signals fOr the purpose of comprising a plurality of aerials spaced apart, bringing the wanted signals arriving from each 50 selective receiving means of such high order of of the aerials into phase agreement. Furtherselectivity as to remove direct interference of more the phase adjusting means may be emplcyed unwanted transmissions from the signals received, to effect a combination of the wanted signals means combining the modulation signals comwhich is not truly arithmetioal, in order to reduce prising the wanted signals and heterodyne beat still further a heterodyne interference resulting,

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for instance from wanted and unwanted signals arriving from closely similar directions.

The invention will further be described with reference to the accompanying drawings in which Figures 1, 2 and 3 show diagrammatically alternative systems for carrying out the invention.

In the drawings four aerials I0, II, I2 and I3 are provided spaced any distance apart (e. g. by a distance of the order of a wavelength of the signals to be received) and in any symmetrical or unsymmetrical arrangement. These aerials may either be non-directional or may beconstructed in any known manner to have directional characteristics for the purpose hereinafter described or again they may each be of the multiple type to minimize the effects of fading. At each aerial there is provided a signal accepting means I4 of any well known form and including in this instance a detector or other equivalent means for isolating the modulation frequencies. The modulation signal output from each of the receivers I4 is conducted by lines I5 to a main receiving station generally indicated at I6. The lines I5 are connected through phase adjusting means I1 for each receiver to a main receiving apparatus indicated at I8 in which the signals received at the several aerials lare combined. The receivers I4 are highly selective for the purpose of eliminating interference as far as is possible and may be such as are described in U. S. Patent No. 1,821,032, dated 1st September, 1931, in order to obtain substantial freedom from interference due to direct reception of the modulation signals of unwanted transmissions,

Thus the selectivity of the receivers I4 may be such that there is no response to interfering signals whereof the carrier frequency lies outside the response curve of the receiver but differs from the'frequency of the wanted carrier wave by an amount less than the highest modulation frequency of the wanted signal. Such a receiver embodies means for correcting the inherent signal distortion due to the high selectivity of the receiver in order that modulations of the carrier wave of the wanted signal corresponding to its whole modulation range may be faithfully reproduced. Alternatively, the receivers may be described as having such high selectivity and/or low damping that there is no response to interfering modulated signals whereof the side band frequencies differ from the frequency of the wanted carrier wave by an amount less than the highest modulation frequency of the wanted signal, modulations of the carrier wave of the wanted signal corresponding to its whole modulation range being faithfully reproduced by the aid of means for correcting the inherent signal distortion due to the high selecticity of the receiver.

It will be understood that the phrase highest modulation frequency is employed to refer to the highest modulation frequency that is considered necessary for the tolerably good or satisfactory reproduction of the signals, as distinct from such higher frequencies as may be present but of which the absence from the received signal is not noticeable. The phrase no response is employed to indicate that the interference from a normally modulated transmission is negligibly small to a normal individual when the wanted and the interfering signals are of comparable field strength.

It can be shown that it is a characteristic of receivers of such high degree of selectivity that the amplitude of the signal response is inversely proportional to the frequency ofthe signal modulation. It is of course necessary to subsequently correct for such distortion.

In operation assuming that the wave front of signals required to be received is moving in the direction indicated by the arrows 20 and that of the interfering signals in the direction indicated by the arrows 2I and for the purpose of explanation that the frequencies of the two transmis-y sions are such that carrier-Waves of the two transmissions heterodyne to produce in a receiver an audible beat note which is objectionable. Under these circumstances each of the receivers I4 which are tuned to select the required signals will also produce beat note interference. Further assuming that at the aerial II the relative phase of the carrier wave of the wanted transmission with respect to that of the unwanted transmission is such as to produce a heterodyne peak at a given instance. Then at the other aerials the phase relationship of the two transmissions will be different depending in this instance solely upon the difference in path of the unwanted and wanted signals. For instance at the aerial I0 the difference in phase will depend upon the distance apart of the aerial I0 from the aerial I I. The wanted signals arrive at the aerials I0 and II simultaneously but the unwanted signals arrive on the two aerials in succession so that if the distance apart of these aerials is for instance half a wavelength of the unwanted signals the resultant beat note produced will be in phase opposition to the beat note received from the aerial II. The phase relationship of the heterodyne beat note received in the separate receivers will differ as between one receiver and another depending on the distribution of the aerials for any given transmissions so that by combining the received signals at a central receiver the heterodyne beat note is suppressed to a large degree. By combining the received signals at the central receiver the wanted signals are added together arithmetically or substantially arithmetically because the phase difference between the modulation signals from the several aerial receivers I4 will be negligibly small except .for a very wide spacing of the aerials and in this latter case the wanted signals may be brought into phase agreement by slight adjustments of the phase correcting devices I1. The heterodyne beat notes will be considerably different in phase and will thus be combined vectorially so that the resultant is zero or some relatively small value.

In an alternative arrangement the signal accepting means indicated at I4 for each aerial may comprise for instance a high frequency amplifier to pass on the high frequency signals to the central receiving station I6 and in this case detection of the signals from each aerial takes place in the main receiver before the signals are combined, for instance in the phase controlling devices I'l. In this arrangement it is important that the paths between the aerials and the main receiver should be the same or alternatively the phase adjusting devices-I1 should be adjusted to compensate for any differences. In the arrangement previously described with reference to Figure 1, in which the modulation signals are transferred from the aerials to the central receiver it is not so essential to control the phase of the signals before they are combined because unless the spacing of the aerials is very large the effect upon the phase of the modulation signals is very small.

In the case of single side band transmissions the carrier may be supplied by means of a locally produced carrier frequency applied to the signals at each of the receiving devices I4, or if a small percentage of carrier is included in the transmitted signals, the receiving devices |4may be of such low damping as to build up this carrier component to the normal value for the received signals.

It will be understood that this suppression of the heterodyne beat note or a plurality of such of the Wanted transmission.

In order further to ensure freedom from heterodyne interference each of the aerials l0, ll, l2 and I3 may be constructed in any known manner suppressing one side band of the received signals, and signal accepting means 42 including a detector for isolating the modulating frequencies. The modulation signal output is conducted by lines to a main receiving apparatus 44 common to all the aerials through phase adjusting means 43. In construction the signal accepting means 42 constitute highly selective receivers for elminiating, as far as is possible, direct interference due to an unwanted transmission, and such highly selective receiving apparatus may be of the form described in the aforesaid Patent No. 1,821,032. 'Ihe loop aerials 40 are adjustable as regards direction in order to provide the best response from Wanted signals arriving in the direction indicated by the arrows 20, and a lesser response from the unwanted signals arriving in the direction indicated by the arrows 2l. The loop aerials 40 are controlled by means of a remote control device 45 located at the main receiver and connected by lines indicated at 46 to the several loop aerials.

In the embodiment of the invention shown in Figure 2 of the drawings each of a plurality of spaced aerials 3D feeds signal selecting means 3| the required signals and the output of the signal selecting is applied to frequency changing means 32 in which the modulation signals are impressed upon a carrier Wave of a frequency different from that of the original carrier wave. The modulated carrier wave output from the device 32 is then applied to a filter 33 for suppressing one side band of the signals and the remaining side band and the local carrier wave is transmitted through a channel indicated at 34 to the central receiving station generally indicated at 35. The channel 34 for each aerial may consist of a conducting line as described with reference to Figure 1 or may be constituted by a wireless link connecting the receiving station at each aerial with the central receiving station 35.

The suppression of one side band of the received signals at the device 33 serves further to reduce any possible heterodyne interference by eliminating any interfering frequency occurring in the suppressed side band.

The central receiving station 35 comprises a highly selective receiving means 36 for the signals from each aerial. This receiving means being for example of the kind described in U. S. Patent No. 1,821,032, dated 1st September, 1931 and comprising essentially a rectifier for isolating the modulation signals. The modulation signals from each of the devices 36 are passed through 31 to a single amplifier before described with reference to Figure 1 and thus provide an output at 39 free from interference.

Instead of combining the signals from the several The heterodyne interference thus obtained may then be opposed to complete signals received on a sepfects will be'added vectorially and thus tend to balance out.

note produced the heterodyne beat interference signals in approximately the same phase for the wanted signals whereby the heterodyne beat interference signals are combined in out-of-phase relationship and with diminished effect.

2. A receiving system for modulating carrier wave transmissions comprising the combination of an aerial, selective receiving means at said aerial tuned for the wanted signals and of such high order of selectivity as to remove modulation interference of an unwanted transmission, at least one additional aerial spaced apart from the first said aerial and also having selected receiving means similarly tuned for the wanted signals and of such high order of selectivity as to remove modulation interference of the unwanted transmission, said additional aerial being so spaced from the rst said aerial that the heterodyne beat note produced by the wanted and unwantedl signals is different in phase at the two aerials, means to suppress one side band of the signals received at each aerial, and means combining the modulation signals comprising the wanted signals and the heterodyne beat interference signals in approximately the same phase for the wanted signals whereby the heterodyne beat interference signals are combined in out-ofphase relationship and with diminished effect.

3. A wireless receiving system for modulated carrier wave transmissions comprising several directional aerials indiscriminately spaced apart, selective receiving means at each aerial similarly tuned for the wanted signals and of such high order of selectivity as to remove modulation interference of the unwanted transmissions, means to suppress one side band of the signals received at each aerial, means combining the modulation signals comprising the wanted signals and the heterodyne beat interference signals obtained from the aerials in approximately the same phase for the wanted signals, whereby the heterodyne beat interference signals are combined in outof-phase relationship and with diminished resultant effect.

4. A receiving system for modulating carrier wave transmissions comprising thecombination of an aerial, selective receiving means at said aerial tuned for the wanted signals, the selectivity of said receiving means being such that there is no response to interfering modulation signals whereof the carrier frequency differs from the frequency of the wanted carrier wave by an amount less than the highest modulation frequency of the wanted signal, at least one additional aerial spaced apart from the first said aerial and also having selective receiving means similarly tuned for the wanted signals and of such high order of selectivity as to remove modulation interference of the unwanted transmission, said additional aerial being so spaced from the first said aerial that the heterodyne beat note produced by the wanted and unwanted signals is different in phase at the two aerials, a receiving station common to the aerials, a frequency converting device at each aerial for changing the frequency of the carrier-wave to another frequency for transfer of the signals to said receiving station, and means at said receiving station combining the modulation signals comprising the wanted signals and the heterodyne beat interference signals in approximately the same phase for the wanted signals whereby the heterodyne beat interference signals are combined in out-ofphase relationship and with diminished effect.

5. A receiving system for modulated carrier wave transmissions comprising the combination of an aerial, selective receiving means at said aerial tuned for the wanted signals, the selectivity of said receiving means being such that there is no response to interfering modulation signals whereof the carrier frequency lies outside the response curve of the receiver but differs from the frequency of the wanted carrier wave by an amount less than the highest modulation frequency of the wanted signal, at least one additional aerial spaced apart from the first said aerial and also having selective receiving means similarly tuned for the wanted signals and of similar high order of selectivity, said additional aerial being so spaced from the first said aerial that the heterodyne beat note produced by the wanted and unwanted signals is different in phase at the two aerials, and means combining the modulation signals. comprising the wanted signals and the heterodyne beat interference signals in approximately the same phase .for the wanted signals, whereby the heterodyne beat interference signals are combined in out-of-phase relationship and with diminished effect.

6. A wireless receiving system for modulated carrier wave transmissions comprising several aerials so spaced with regard to the direction and wave-length of wanted signals and unwanted signals that heterodyne beat effects between wanted and unwanted signals are in different phase at at least two of the aerials, selective receiving means at each aerial similarly tuned for the wanted signals, the selectivity of said receiving means being such that the amplitude of the modulation frequencies of the wanted signals throughout the whole of the modulation frequency range is relatively altered, said receiving means including devices for relatively altering the amplitude of the modulation frequencies in the opposite sense, and means combining the modulation signals comprising the wanted signals and the heterodyne beat interference signals obtained from the aerials in approximately the same phase for the wanted signals, whereby the heterodyne beat interference signals are cornbined in out-of-phase vrelationship and with diminished resultant effect.

'7. A wireless receiving system for modulated carrier wave transmissions comprising a plurality of aerials disposed in spaced relation, and means u whereby wanted modulation signals intercepted by said aerials are combined in approximately the same phase and are reproduced while heterodyne beat notes between wanted and unwanted signals intercepted by said aerials are combined in different phase and substantially eliminated, said last named means including selective receiving means for the signals from said aerials, the selectivity of said receiving means being such that there is no response to interfering modulation signals whereof the carrier frequency of such interfering signal differs from the carrier frequency of the wanted signal by an amount less than the sum of the highest modulation frequencies of both signals.

8. A wireless receiving system for modulated carrier wave transmissions comprising a plurality of aerials disposed in uniformly spaced relation, and means whereby wanted modulation signals intercepted by said aerials are combined in approximately the same phase and are reproduced while heterodyne beat notes between wanted and unwanted signals intercepted by said aerials are combined in different phase and substantially eliminated, said last named means including selective receiving means for the signals from said that there is no response to interfering modulaaerials, the selectivity of said receiving means tion signals whereof the carrier frequency difbeing such that there is no response to Vinterfers from the frequency of the wanted carrier vfering modulation signals whereof the carrier wave by an amount less than the highest modufrequency of such interfering signal differs from lation frequency of the wanted signal, and means the carrier frequency of the wanted signal by an combining the modulation signals comprising the amount less than the sum of the highest modula- Wanted signals and the heterodyne beat intertion frequencies of both signals. ference signals obtained from the aerials in ap- 9. A wireless receiving system for modulated proximately the same phase for the Wanted sigcarrier wave transmissions comprising several nals, whereby the heterodyne beat interference aerials disposed in uniformly spaced relation in signals are combined in out-of-phase relationa straight line, selective receiving means at each ship and with diminished resultant effect. aerial similarly tuned for the wanted signals, the selectivity of said receiving means being such JAMES ROBINSON. 

